BBC (Feb. 21) – Even though the Big Bang happened 13.8 billion years ago, scientists have a good understanding of the nuclear reactions that produced the first elements. Satellites have taken precise measurements of what the early universe was like, allowing researchers to calculate exactly how much of each element and isotope should have been made. But when researchers compare their calculations with what they observe, not everything matches. “The deuterium is bang-on,” says Brian Fields, an astrophysicist at Illinois. “The helium is looking good. Lithium is the one that's off.”